We can't have standards because even that is subjective to the person listing things.

You idea of lightly stained may be someones ideas of badly stained. Someones badly stained diaper may be someones idea of lightly stained. And cameras don't always show the stains no matter how many times you try to get a picture of it.

Smell is also subjective. Some people can't smell perfumes and such as well as others. So while one person would swear up and down that it doesn't smell another person would say it does.

Going by what the OP put down as her standards (which isn't how I'd define those abbreviations in some instances) what does 'showing slight signs of wear' vs 'showing moderate signs of wear' mean? What is slight wear to one person is moderate wear to another. What is moderate wear to one person is heavy wear to another.

So what I'd personally recommend is not buying something that only uses an abbreviation unless you ask a lot of specific questions. That reduces the likelyhood of being surprised by the condition of something you buy.